[llvm-dev] cuda __shfl_sync problem

[George K via llvm-dev]

Do you mean in llc? Because i don't see such an option i'm afraid.

~George

On 24-09-2020 20:54, Johannes Doerfert wrote:
> Not that I am an expert but it looks like it defaults to the minimal 
> PTX version that supports the compute capability. You might be able to 
> choose PTX 6.0 though.
>
> ~ Johannes
>
>
> On 9/24/20 1:02 PM, George K via llvm-dev wrote:
>> Hi,
>>
>> First of all, i'm not sure if i should be posting this here or in 
>> cfe-dev, but here it goes.
>>
>> In order to instrument CUDA kernels i first generate device IR with:
>>
>> clang++ -x cuda --cuda-device-only -emit-llvm --cuda-gpu-arch=sm_52 
>> -o device.bc
>>
>> I also have a library that contains the instrumentation stubs for 
>> which i generate IR similarly and i link it with the device IR 
>> programmatically with Linker::linkModules(..)
>>
>> Then after some analysis i use llc to get ptx:
>>
>> llc device.bc --march=nvptx64 --mcpu=sm_52 --filetype=asm -o device.ptx
>>
>> This works fine but the problem is that the instrumentation code uses 
>> __shfl_sync() and ptxas gives me the following error:
>>
>> ptxas device.ptx, line 1033; error   : Feature 'shfl.sync' requires 
>> PTX ISA .version 6.0 or later
>>
>> Now according to 
>> https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#warp-shuffle-functions,
>>
>> __shfl_sync is supported by compute capability >= 3 and according to 
>> https://developer.nvidia.com/cuda-gpus#compute my GTX950 has Compute 
>> Capability 5.2.
>>
>> Also according to 
>> https://docs.nvidia.com/cuda/parallel-thread-execution/index.html#release-notes 
>> PTX ISA 6.0 does support sm_52.
>>
>> However llc generates:
>>
>> .version 4.1
>> .target sm_52, debug
>> .address_size 64
>>
>> Any ideas why this is happening? Or am i doing something wrong?
>>
>> PS. I'm using CUDA 10, driver 440
>>
>> ~George
>>
>>
>>
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